Vane tracking in hydraulic pumps



Dec. 2, 1969 c. E. ADAMS ET AL 3,481,276

VANE TRACKING IN HYDRAULIC PUMPS Dec. 2, 1969 c. E `ADAM5 ET AL 3,481,276

VANE TRACKING IN HYDRAULIC PUMPS Filed Nov. 27, 1967 7 Sheets-Sheet 2 PRESSURE zoNE sa Dec. 2, 1969 c, E, ADAMS ET Al.

VANE TRACKING IN HYDRALIC PUMPS 2.? a Wi@ gil/'225 M 7 Sheets-Sheet 3 Filed Nov. 27, 1967 Dec. 2, 1969 c. E. ADAMS ET AL 3,481,276

VANE TRACKING IN HYDRAULIC PUMPS Filed Nov. 27, 1967 7 sheets-sheet 4 ROTATION SUCTION RAMP MINO R DIAMETER E ssuRE PRE RAMP Dec. 2, 1969 c, E. ADAMS ET-AL 3,481,276

VANE TRACKING IN HYDRAULIC PUMPS Filed Nov. 27, 1967 '7 Shee'cS-SheefI 5 4 SUCTION MAJOR Y PRESSURE MINOR RAMP DIAMETER RAMP DIAMETER 0- FIG.I3 BACKPRESSURIZING ZONE CAM coNToU I NQMSLPMI I f POCKET x PATH OF VANE ,f DURING SKIPPING RADIALv DISPLACEMENT OF VANE V VANE MOVEMENT l REA INCREASE T i o VOLUM OF PISTQN PRESSURE CII'IIMBER I I T T PRESSURE- T SIFIQATIQN ABQVE MINIMUM PRESSURE P CHAMBER 7| MINIMUM PRESSUREI IN CHAMBER 7| ABOVE OUTLET PRESSURE BACKPRESSURE @del RADIAL VELOCI'I INSUFFICIENCY RELATION TO CIN VANE ACTUATING MEANS PQINT OF VANE IMPACT VELOCITY OF VANE DURING SKIPPING Y OF VANE DF CENTRIFUGAL FORCE AT IDLING CONDITIONS IN REQUIRED RADIAL ACCELERATION LEADS TO SKIPPING CENTRIFUGAL FoRc oN VANE THRU suc'rl N RAMP Y INI/.Mmes REQUIRED RADIAL AccELERATloN oF VANE mmd, THRU sUcrIoN RAMP Ml/y- MW Mm ,6g/m

aff//VXS c. E. ADAMS ET AL 3,481,276

VANE TRACKING IN HYDRAULIC PUMPS 7 Sheets-Sheet G Dec. 2, 1969 Dec. 2, 1969 c. E. ADAMS ET AL 3,481,276

VANE TRACKING IN HYDRAULIC PUMPS Filed Nov. 2'?. 1967 7 Sheets-Sheet 7 United States Patent O 3,481,276 VANE TRACKING IN HYDRAULIC PUMPS Cecil E. Adams, Columbus, Randall E. Griilith, Galena, and Charles R. Miller and Jack W. Wilcox, Columbus, Ohio, assiguors to Abex Corporation, New York, N.Y., a corporation of Delaware Filed Nov. 27, 1967, Ser. No. 685,784 Int. Cl. F04c 1/00, 1 7 00; F01c 1/00 U.S. Cl. 10S-136 24 Claims ABSTRACT F THE DISCLOSURE A method and structure for eliminating improper tracking or vane skip over part of the cam surface, e.g. the suction ramp, when the pump is operating at very low outlet pressure, by intermittently directing a small portion of the pump outlet volume through flow restricting means to establish a temporary backpressure in the betweenvane pocket adjacent the ilow restricting means. The 'backpressure thus developed automatically replenishes the supply of tiuid in a chamber connecting inner actuating surfaces associated with the vanes, the pressure in which chamber provides outward force on the inner actuating surfaces of the vanes suicient to hold the vanes in contact with the cam surface. The remainder of the total output volume is delivered to the outlet port without passing through the ow restricting means.

This invention is broadly directed to hydraulic vane pumps, and more specifically to hydraulic vane pumps of the type which include hydraulic means for vane control.

Vane pumps commonly include a rotary member or rotor having a plurality of vanes carried in slots around its periphery. The vanes are urged against the inner or cam surface of a xed stator or cam ring which surrounds the rotor. Suction and pressure ports open at spaced positions into the pumping chamber between the periphery of the rotor and the inner surface of the cam ring and are swept or traversed sequentially by the vanes as the rotor is driven by a prime mover. The space between each two adjacent vanes defines a transport pocket in which uid is conveyed from the suction port to the pressure port. At the suction port the cam surface has a4 suction ramp where it diverges from the rotor periphery,

and as the volume of a transfer pocket is increased by this divergence, uid is taken into the pocket through the suction port. The pocket transports the Huid therein across a transfer zone to the pressure port. Adjacent the pressure port the cam surface has a pressure ramp across -which it converges with the rotor periphery, and as the vanes are cammed inwardly by the pressure ramp the volume of the pocket is decreased so that fluid is displaced therefrom through the pressure port.

In order to provide the most eflicient pumping action, the vanes must properly track on the cam surface, that is, they be maintained in sealing engagement with the cam surface as the rotor rotates. Centrifugal force acting on the individual vanes due to rotor rotation urges the vanes outwardly, and if the rate of rotation is high, this is sometime suicient to effect the seal. However, since the pump may be called upon to operate at low speeds of rotation, or with high viscosity uids, and since a dirt particle or a close it of the vane in its slot may impede outward vane movement, centrifugal force alone is ordinarily considered insuiiicient to assure establishing and maintaining continuous sealing contact of the vane edge with the cam surface.

' For this reason vane actuating means are commonly used to provide additional outward force. Springs can be ICC employed for that purpose. However, because of the relatively limited and confined space in the rotor in which springs can be disposed for actuating the vanes, the springs have to be small, and may not always provide suicient actuating force. Moreover springs are subject to fatigue and relaxation, and this tendency, especially in high performance pumps, is leading the art away from the use of springs.

This invention is applicable to vane pumps of the type wherein the vanes are hydraulically actuated toward engagement with the cam surface; that is, a iiuid pressure force is applied to an inward facing vane surface, so that the force acts on the vane in a direction tending to move the vane toward the cam surface.

The hydraulic actuating means used may be either of the so called two area type or may be of the three area type. In each case a fluid force is applied to a surface associated with the individual vane, to act thereon in the direction toward the cam surface. Where the hydraulic actuating means is of the two area type, the two areas referred to usually comprise the inner and outer ends of the vane. A uid force is applied to the inner edge of the vane, which tends to move the vane outwardly against a smaller, oppositely directed force that acts on the outer edge or tip of the vane. The net force acts outwardly to provide vane actuation.

In vane pumps of the three area type, fluid pressures act on three areas associated with each vane, and the forces resulting from these pressures cooperate to urge the vane toward the cam surface with a predetermined desired force. The pressure acting on two of the areas associated with each vane are substantially equal but act in opposite directions, and the forces resulting from these pressures tend to counteract each other. The first area comprises a surface on the outer end of the vane, and is subjected to pressure which urges the vane inwardly. The second vane area is an inwardly facing Vane surface which is subjected to a pressure opposed to that acting on the rst area, and urges the vane outwardly.

The third area associated with each vane is also inwardly facing and is subjected to pressure to urge the vane outwardly to maintain the fluid seal between the outer end of the vane and the cam surface. One form of a three area vane pump having hydraulic actuation for the vanes is that shown in Adams et al. Patent No. 2,832,293, titled Vane Pump, of which one of the present inventors is a co-patentee. As shown in that patent, a piston-mounted in the rotor is associated with each vane, and is slidable in a radial direction to engage the inner end of the vane. The sectional area of the piston denes the third area in this instance. Fluid under pressure for actuating the several pistons is supplied through a chamber in the rotor which is in turn fed through a channel formed in the stationary cheek plate at the side of the rotor and leading from the high pressure zone.

Adams et al. Patent No. 3,223,044, of which one of the present inventors is again a co-patentee, shows a valved three area construction in which the rotor assembly has an internal lpressure chamber into which pressure fluid is supplied through check valves in the rotor from a high pressure zone of the pump when the pressure in the chamber tends to drop below the pressure in the high pressure' zone. As shown in that patent, the third area means may for example comprise a piston having an axial passage and an outer end which forms a check valve with the inner end of the respective vane, to govern the admission of pressure uid from a pressure zone into the chamber interconnecting the inner ends of the pistons. Whenever the external pressure in the vane slot exceeds the pressure in the internal chamber tending to hold the piston valve closed, pressure uid in the vane slot pushes the piston away from the vane, thereby opening the valve and flows into the chamber through the longitudinal passage in the piston until a substantial pressure equilibrium is reached. This pressure force acts equally on all the pistons and is applied through the pistons to the vanes to urge them against the cam surface.

Vane pumps provided with hydraulic vane actuation, especially of the three area type, are generally effective in maintaining sealing contact between the vane and the cam surface during the pumping cycle. However, in long eX- tended use of such pumps, it was noted that chop marks began to appear on the cam surface. These usually appeared in the downstream half of the suction ramp.

Although the pump was operating satisfactorily, the chop marks were indicative of an incipient irregularity starting to form on the pump cam ring, which would accelerate vane and/or cam ring wear and ultimately reduce pump life.

The actual path of movement of pump vanes while operating was investigated through a special window in the cheek plate using stroboscopic light to stop the motion. The'se studies showed that the chop marks were resulting from the impact on the suction ramp of vanes which were ski-jumping or skipping across the first part of the suction ramp on the cam surface. In the suction ramp the cam surface diverges quite rapidly from the rotor surface, thereby increasing the volume of the transfer pockets to receive incoming fluid. Investigation indicated that the vanes were not accelerated outwardly rapidly enough to maintain contact with the suction ramp as it diverged; in other words, the vanes were under insufficient force to follow the outward path of the suction ramp as they rotated rapidly over it. Further study showed that this phenomenon generally occurred not under heavy load, but rather when the pump was idling, that is, when the outlet pressure was of the order of 150-200 p.s.i. or lower. Such conditions occur in use When there is no externally applied or internal load on the hydraulic circuit or system to which the pump is supplying uid.

Our experiments indicated that at such conditions, the low output pressure is insufficient to provide the force on the hydraulic actuating means necessary to accelerate the vane outwardly rapidly enough to maintain contact with the cam ring. Hence, the problem was to provide sucient pressure within the pump even when the pump is delivering essentially no output pressure, to supply the hydranlic force on the vane actuating means necessary to avoid vane ski-jumping over the suction ramp.

One possibility would have been to impose a restriction on flow through the outlet port to choke it and thereby create a back pressure within the pump. However, analysis shows that this would require excessive horsepower even at idle (for example, four additional horsepower), and would quickly result in overheating of the oil unless special cooling means were provided. That approach is therefore economically unacceptable. As an alternative, we attempted to establish a pressure differential between the inner and outer ends of each vane by restricting ow therebetween. That resulted in an undesirably large force being applied to the vanes over other phases of the' pumping cycle; the force on the vanes as they traverse the transfer zones, the pressure ramps and the sealing zones was much greater than necessary to maintain a seal at those areas. This led to much more severe vane tip Wear. Ultimately the present method was discovered, which overcomes the foregoing problems.

In accordance with this invention, a small portion of the fluid in the transfer pocket is momentarily displaced through flow restricting means ahead of the outlet port so that a transientbackpressure is established in that pocket which is higher than the pressure on the outlet volume' at the outlet port. That backpressure is applied to the hydraulic actuating surface associated With the vane to hold the vane into contact with the cam surface over the suction ramp.

CII

We have found that the required force can be established with only a minor portion of the pump output volurne which can be as low as 10% or less of the total volume. The cost in horsepower terms is negligible. Skipping at the' suction port is prevented without undesirable secondary effects.

In preferred embodiment the invention is carried out by directing a small proportion of fluid from the fluid transport pocket through a flow restrictor as the pocket approaches but before it actually comes into unrestricted communication with the pressure port. After passing through the flow restrictor, this small ow is mixed with the remainder of the output volume downstream of the cam pressure port. The restrictor is shaped to provide a substantially constant back pressure on fluid in the transfer pocket while the displacement through the restriction is occurring, and this pressure is applied to vane actuating means of the three-area type to provide force on other vanes which are then at the suction ramp, suflicient to prevent skipping. Tests have shown that virtually continuous vane tracking is achieved even at outlet pressures at which comparison pumps had evidenced ski-jumping at the suction ramp. Tests further verify that the cost in horsepower is insignificant and that the life of the pump is significantly extended.

The further objects and advantages of the present invention will be apparent from the following detailed description, reference being made to the accompanying drawings wherein a preferred embodiment of the invention is shown.

In the drawings:

FIGURE l is a vertical longitudinal or axial section of a preferred form of vane pump including the invention;

FIGURE 2 is a half section taken on line 2 2 of FIG- URE 1;

FIGURE 3 is a transverse section taken on line 3 3 of FIGURE 1 and shows the relative positions when the backpressurizing phase of the pumping cycle is just starting;

FIGURE 4 is a transverse section similar to FIGURE 3, but shows the relative positions when the backpressurizing phase is just ending;

FIGURE 5 is an enlarged fragmentary transverse section showing a vane in the rotor as it is traversing a transfer zone;

FIGURE 6 is an enlarged section similar to FIGURE 5 but shows the vane as it is traversing a sealing zone;

FIGURE 7 is a perspective View of a vane of the type shown in FIGURES 5 and 6;

FIGURE 8 is a plan View of a Iearn ring or stator superimposed on a polar graph to illustrate the several operating segments of the cam surface thereof which constitute the major and minor diameters and the pressure and suction ramps;

FIGURE 9 is a plan view, reduced in size, of the opposite or reverse side of the cam ring shown in FIGURE 8;

FIGURE 10 is a transverse section taken on line 10-10 of FIGURE 1, and shows the front cheek platej FIGURE 11 is a transverse section taken on line 11-11 of FIGURE l, and shows the rear cheek plate;

FIGURES 12A through 12E are a series of graphs which show, as function of vane position with respect to the cam surface, the radial displacement of the vane, the volume of the piston pressure chamber, the ba'ckpressure on the vane actuating means, the radial velocity of the vane, and the centrifugal force and required radial acceleration of the vane in a pump of the type shown in FIGURES 1-11;

FIGURE 13 is a graph illustrating the rate of displacement of fluid from a transport pocket during the backpressurizing phase of the pumping cycle; and

FIGURE 14 is a transverse section, somewhat diagrammatic in nature, showing the cam ring and rotor of a vane pump of the two-area type including the invention.

and an end cap 2 having a rim or flange 3 which telescopes into one end of the body and is sealed thereto by an O-ring 4. The body and end cap are connected by bolts as shown in FIGURE 2.

The front end wall 5 of cap 2 has an opening through which the pump operating shaft 6 extends. Shaft 6 is supported for rotation by a -ball bearing 7 `which is secured against axial movement in the opening. A flexible seal 8 prevents the leakage of oil along shaft 6. The shaft extends into body 1 from end cap 2, and at its rear or inner end is carried for rotation by a needle roller bearing 9 mounted within a central bore in the body.

The end cap 2 supports and is sealed around a front cheek plate 10 having a smooth, flat inner surface 11 which bears against a side or radial face 13 of an annular cam ring 14. On its opposite side surface 17, cam ring 14 in turn bears against a smooth ilat surface 18 of a rear cheek plate 19 and clamps the latter cheek plate against an internal shoulder in body 1. It may be mentioned here that the cam ring itself as well as the housing and cam ring together are sometimes referred to in the art as a stator. The cam ring is clamped between the two cheek plates by four bolts, not shown, which pass through bolt holes 20 (FIGURE 3) in the cam ring which are aligned with holes 21 (FIGURE l0) in both cheek plates 10 and 19.

A fluid intake passageway 22 extends radially into body 1 and communicates with a pair of internal annular channels 23, 24 which encircle the internal cavity within the body. These annular channels 23, 24 distribute fluid from the intake passageway 22 to suction ports in the cheek plates, to be described.

The cam ring 14 is supported radially by an annular rib 26 formed in the body 1 between the annular channels 23, 24. The cam ring encircles a rotor 28 which is connected to and driven by shaft 6 through splines 29. The spline joint permits proper running alignment of the rotor between the opposed flat surfaces 11 and 18 of the front and rear cheek plates respectively. Both cheek plates have central openings through which shaft 6 passes. The rotor has a plurality of radial vane slots 31 (FIG- URE 3) in each of which a vane is mounted.

The cam ring 14 has an inward facing cam surface 34 that is contoured to provide a balanced or symmetrical pump construction in which there are pairs of diametrically opposite low pressure, inlet or suction zones 36,

ltransfer zones 37, high pressure, outlet or exhaust zones 38, and sealing zones 39` between the cam surface 34 and the rotor 28, as designated in IFIGURE 3. In order to provide the opposed zones, cam surface 34 is formed in part from a first pair of arcs which extend across the liuid transfer zones 37. While these arcs define what is frequently called the major diameter part of the cam surface (see FIGURE 8), they have a slight ramp or in- Ward lead in the direction of rotation. A second pair of arcs of shorter radii than the major diameter arcs extend across the sealing zones 39 and define the minor diameter portion of the cam surface. These pairs of arcs are interconnected by suction ramps and pressure ramps which extend across the low and high pressure zones 36 and 38 respectively Such cam surface configurations are old in the art and do not constitute the present invention.

Together the rotor and vanes constitute a rotatable cartridge within the stator. The outer edges of the vanes engage and maintain contact with the cam sur- `face 34 of cam ring 14, and the side edges of the vanes slide over the smooth at surfaces 11 and 1,8 of the front and back cheek plates on opposite sides of the rotor. Thus the pairs of adjacent vanes divide the pumping space between the rotor, cam surface, and cheek plates into a series of pockets for receiving, transporting, or displacing fluid from the inlet port to the outlet port. A pocket is designated at 40 in FIGURE 3.

Intake passageway 22 communicates via the annular channels 23, 24 around cam ring 14 through passages cored in the cheek plates 10 and 19, to pairs of suction ports spaced 180 apart in surfaces 11 and 18 thereof. Two suction ports 43 and 44, best seen in FIGURE 10, are formed in front cheek plate 10 and are fed through channel 2-4, and two additional suction ports 45 and 46 are formed in rear cheek plate 19 (see FIGURE 1l) and are fed through channel 23. These four suction ports are identical in shape at the cheek plate surfaces 11 and 18, and are aligned with the suction zones 36 between the rotor and cam surface. Each suction port is also connected, through a branch passage 47, with a port 50 positioned to come into communication with the inner ends 48 of the vane slots 31 as the rotor turns.

As shown in FIGURE 10, the front cheek plate 10 includes two diametrically opposed pressure ports 51, 52. These ports are preferably T-shaped in the plane of cheek plate surface 11, in order to impart cam ring reversibility and consequently to permit changing the direction of rotation of the pump, as will be explained. The pressure ports are spaced substantially from the suction ports 43 and 44, and they open into the pressure zones 38 between the rotor and the cam surface. It is to lbe noted, in FIGURE 3, that the leading edge of each pressure port is downstream of the start of the cam ring pressure ramp.

The pressure ports 51 and 52 are connected through internal passageways 54 and 55 in cheek plate 10 and end cap 2, to a fluid outlet or delivery coupling 56. In use, coupling 56 is connected to an external hydraulic circuit, not shown.

Each T-shaped pressure port 51 and 52 is in effect extended to the end of the pressure ramp that is adjacent the sealing zone by a cooperating semi-circular recess 59, 60, formed on cam ring side surfaces 13 and 17 (see FIGURES 2, 3, 8, and 9). Each recess 59 and 60 opens to the pumping space around the cartridge immediately downstream of the respective cheek plate pressure port, in pressure zone 38.

The cam ring is aligned with respect to the two cheek plates by a dowel pin 61 on each face 13 and 17 of the cam ring. This dowel pin is registrable in either of two holes 62, 63 in each of cheek plate surfaces 11 and 18 of the cam ring. The holes y62 and -63 are spaced 90 from one another, so that the direction of rotation of shaft 6 can be reversed, when the pump is disassembled, by turning the cam ring about an axis transverse to its own axis and orienting the dowel pin with the other holes `63 or 62 in the cheek plates.

The cam ring recesses 59 and 60 are provided to effect for such reversibility of the pump, and they extend the cheek plate pressure ports 51 and 52 to the end of the pressure ramp that is adjacent the sealing zone, regardless of the direction of shaft rotation.

In the direction of rotor movement as shown by the arrow in FIGURE 4, the suction ramp portion of cam surface 34 progressively recedes from the periphery of the rotor 28 across each suction zone 36, so that the volume of a transport pocket 40 between the vanes is increased in that zone.

Across the transfer zones 37 the major diameter part of cam surface 34 very slightly approaches the rotor, and across the pressure zones 38 the pressure ramp more steeply approaches the rotor 28 as it comes into close proximity with the rotor periphery in the sealing zones 39. Thus, the radial displacement of a vane is shown graphically in FIGURE 12A. Fluid is drawn into a transport pocket 40 through the suction ports as the pocket becomes larger in moving across the suction zones 36, and most of the Huid in the pocket is displaced as the pocket volume diminishes as the pocket moves through a pressure zone 38, thereby effecting a pumping action.

Each vane 32 is provided with deep grooves 67 which are formed in its outer end and its opposite side edges. The grooves 67 insure that the fluid pressure acting on the first area or outer end surface of the vane will be substantially balanced at all times by the pressure in vane slot `48 acting on the second area or inner end surface 79 of that vane.

For the pump to operate at high efficiency it is necessary to maintain a continuous sealing engagement of the vane tip with the cam surface 34, regardless of changes in the arcuateness of the cam surface. In this connection, it may be noted that, Where a double lip vane of the type illustrated by way of example in the drawings is employed, only the front or leading lip of the vane will engage the pressure ramp (see FIGURE 3) while only the rear or trailing lip will engage the suction ramp.

To provide the hydraulic actuating pressure on the vanes, one or more radial bores or piston cylinders 69 is formed in rotor 28, extending inwardly from the rounded inner end 48 of each vane slot 31. The bores 69 are interconnected at their inner ends through an annular accumulator or piston pressure chamber 71. Apart from any minor leakage, fluid can fiow into and out of pressure chamber 71 only through radial bores 69.

The pressure chamber 71 is constructed, in part, by an annular groove 72 in rotor 28 and a smaller groove 73 formed in a sleeve 74. The sleeve is fitted and sealed, as by welding or brazing, in a central opening in rotor 28, to define pressure chamber 71.

A generally cylindrical pin or piston valve element 76 is received in each radial bore '69. Each piston 76 includes an axial bore 77 (see FIGURE 5) and is slidable in its cylinder 69 with which it is closely fitted so that leakage of fluid along the external wall of the piston is negligible. The outer end of each piston 76 is conically tapered as at 78 and forms a valve With the flat inner edge surface 79 of each vane 32. The inner end surface of each piston is preferably chamfered as at I80, and presents the hydraulic actuating surface or third area on which the fluid pressure force Iwithin chamber 71 acts to urge the piston against the inner edge surface 79 of the respective vane. The admission of uid to chamber 71 is regulated by the balance of forces between the fluid pressure force acting inwardly upon the piston conical taper 78, tending to move the piston away from the vane, and the opposing force arising from the huid pressure in chamber 71 and the centrifugal force, tending to move the piston toward the vane. The length of the piston 76 is such as to permit it to move into and out of engagement with vane edge surface 79 regardless of the radial position of the vane in its slot.

In operation, the piston and vane cooperate to form a valve 78, 79 which functions in the manner of a check valve to apply pressure fluid to and fill chamber 71 and to prevent reverse ow out of the chamber. When fiuid pressure at the inner end 48 of a vane slot acting upon the conical taper 78 of the piston 76 sufficiently exceeds the pressure in chamber 71, the piston is moved inwardly in its bore `69 and valve 78, 79 opens. Pressure uid in the inner end 48 of vane slot 31 flows inwardly through bores 77 and 69 toward chamber 71 and restores, maintains, or increases the uid pressure in the pressure chamber as necessary to balance the fluid pressure acting to open the valve 78, 79. This action occurs when the vane slot 31 is in a zone in which pressure is sufficiently higher than the pressure in chamber 71 to open the valve. Such hollow piston valves for vane actuation are described more completely in the previously mentioned Adams et al. Patent No. 3,223,044.

Each vane 32 is preferably provided with a channel or groove 82 on its downstream or trailing side. As seen in FIGURE 7, this channel extends from the inner or lower end 79 of the vane, toward but not to the trailing upper lip 83 of the vane. Rotor periphery 64 has a raised central rim 84, as viewed in transverse section, and channel 82 forms a valve Vwith the rotor periphery rim 84 as shown in FIGURES 5 and 6. This valve is open when the vane is extended from the rotor,-as when the rotor is traversing a transfer zone 37, and is closed when the vane is not far extended from the rotor, as when the vane is traversing a sealing zone 39.

Such fiuid diverting channels are described in more detail in the copending application of Adams and Griffith, Ser. No. 490,220, now Patent No. 3,359,914, of which two of the present inventors are the co-applicants. The channels 82 do not of themselves constitute the present invention. However, in pumps incorporating the structure of this invention, the provision of such channels is desirable, for we have found this provides significantly better operation.

As previously indicated, this invention is directed toward backpressurizing, or providing greater than outlet pressure on, the hydraulic vane actuating means in order to establish force sufficient to prevent ski-jumping or skipping of the vanes across the suction ramp at times when normal outlet pressure would be too low. In the preferred embodiment disclosed herein for purposes of illustration, this is accomplished by momentarily displacing a small portion of the fluid in each transport pocket, in sequence, through flow restricting means, and applying the backpressure so developed into piston pressure chamber 71 to act on all the hydraulic actuating means comprised by the pistons 76. Pressure in the chamber 71 thus acts on the pistons of vanes which are traversing the suction ramp, and prevents skipping of those vanes.

The flow restricting means are preferably formed in the front cheek plate as shown in FIGURE 10. Specifically, a small fixed orifice or flow restricting passageway 88 is bored in front cheek plate 10 at a position just ahead -of the beginning of the pressure zone (see FIG- lURE 3). This hole 88 is internally connected to passageway -54 which in turn leads to the outlet coupling 56 (see FIGURES 1 and 2). Hole 88 is counterbored to a larger diameter 89 at the face 11 of cheek plate 10, and a tapering V-groove or bleed slot 90 extends from Counterbore 89 so that it preferably just comes into communication with the slot 67 of one vane when the next trailing vane has just sealed the intervening pocket from the suction port (see FIGURE 3). Counterbore 89 and bleed slot 90 are radially positioned so that both open into the pumping space between the rotor periphery 64 and the cam surface 34.

A second, larger sectioned, flow orifice 91, also in the form of a tapered V-groove, extends from the leading edge of each pressure port 51 and 52 to a point such that it just comes into communication with the vane edge groove 67 when the leading lip cornes onto the pressure ramp (see FIGURE 3). Ideally the periphery of counterbore 89 is spaced circumferentially from the apex or tip of tapered groove 91 by distance equal to the width of the leading lip of a Vane.

It is important to point out that the flow restrictors 88 and 91 are needed only on the upstream side of each pressure port. However, for purposes of reversibility, a similar and corresponding set of fixed restrictors 88, counterbores 89, bleed slots 90, and tapering restrictors 91 are provided on the -other side of each pressure port 51, 52 (see FIGURE l0) for symmetry, to provide similar operation when the cam ring is reversely oriented for opposite shaft rotation. Thus, in a pump which is to operate only in one direction, it is unnecesary to provide such ow restricting means on the downstream side of the pressure port, and the cheek plate pressure port itself can have a length equal to the effective length provided in the construction illustrated by the cheek plate port and the cam ring recess together.

Since fluid is displaced to outlet coupling 56 only through the front cheek plate but not through the rear cheek plate in the embodiment shown, there need be no pressure port on the rear cheek plate. However, it is desirable for purposes of pressure equalization, that blind bleed slots 93 be provided in surface 18 of the rear cheek plate 19,` at positions generally corresponding with the bleed slots 90 on the front cheek plate. The V-grooves 93 on the rear cheek plate may conveniently be stopped or terminated in the direction of rotation by a shallow blind hole 94. These bleed slots 93 do not comprise a part of the backpressurizing structure to which this invention is directed, and they may be omitted, but their use is desirable simply to provide gradual equalization of pressures across the vane lips at such positions.

The fixed area flow restrictors 88 and the varying area ow restricting grooves 91 both provide restricted passages through which fluid is displaced fr-om each transport pocket as that pocket approaches but before the pocket actually breaks into direct communication with the cheek plate outlet port 51 and 452. In this connection, note that the leading edge of each pressure port is downstream of the imaginary line between the axis and the start of the pressure ramp (FIGURE 3). (The forward part of the top of the T does not open into the pressure zone, and is provided merely for better communication with the ram ring recess S9 and 60 when the direction of rotation is reversed.)

The displacement of iiuid through these flow restrictors from each transport pocket lasts for only a moment but while it lasts creates a pressure differential across the restrictors in sequence as the pocket moves forward. At low outlet pressures, flow through the restrictor establishes a pressure differential, so that the uid in the pocket during that moment is under higher pressure than the pressure at the outlet port which is on the downstream side of each restrictor.

This backpressurizing of the fluid in a given transport pocket begins when the pocket designated 40 is approximately at the position shown in FIGURE 3, that is, when the front edge of the trailing vane of the pocket has just sealed the suction port, and the fixed restrictor 88 has just come into communication, through bleed slot 90, with the pocket through the side groove 67 of the leading vane. Both vanes of pocket 40 are riding on their front lips, because of the slight ramp on the major diameter in the transfer zone. This ramp diminishes the volume of the pocket, preferably at an approximately constant rate as the pocket approaches the pressure ramp (note FIGURE 12A). It is this reduction in volume of the transfer pocket which causes fluid to be displaced therefrom, first through the restrictor 88, then through restrictor 91. The resulting or increased pressure is reflected or applied though the side gooves 67 and groove 82 on the vane into the inner end 48 of the vane slot, and will cause the valve 7 8, 79 to open and fill or replenish the supply of uid in the chamber 71 as necessary.

Preferably, during the time when both vanes (between which the transport pocket 40 is defined) are in contact with the major diameter of the cam surface the rate of displacement of fluid from the pocket is essentially constant, as shown in FIGURE 13. This fluid is displaced through Ithe iixed area restrictor 88, so that the ow causes a substantially constant pressure drop across the restrictor. Thus the backpressure in pocket 40 is approximately constant. When the upstream vane comes onto the pressure ramp, it is displaced inwardly at an increasingly greater rate (see FIGURE 12D), and the rate of iiuid displacement from the pocket also increases. In order to prevent this increased rate of displacement from causing an unnecessarily high backpressure, we have found it desirable to provide the second variable area liow restrictor 91, so that as the displacement increases, an increasingly larger ow area is provided by the taper on restrictor 91, to maintain a substantially constant backpressure.

As this backpressurizing is occurring in one pocket, other vanes are traversing the suction ramp (see FIGURE 3). The pressure in chamber 71 acts on all of the vane actuating means, including those associated with vanes on the suction ramp, and prevents skipping.

The magnitude of the backpressure which is established can be controlled by proper selection of the area of ow restrictors 88 and 91.

When the pump is operating under load the system pressure will itself usually provide suiiicient force on the vane actuating means to insure constant vane tracking. However, where the system pressure is low or essentially zero, for example where the pump is idling and is not developing pressure against a work load, such low output pressure may be insuicient to provide the large radial acceleration of the vane required for proper tracking on the suction ramp, even with the assistance of centrifugal force (see FIGURE 12E). Backpressure established should ideally be just slightly larger than the minimum necessary to insure proper tracking when the pump is under no-load conditions. We have generally found that pressures of the order of 10G-200 p.s.i. are sufficient under normal operating conditions, and the restrictors 88 and 91 should be sized with that objective in mind.

Backpressurizing of the transport pocket 40 is terminated, in the preferred embodiment of the present invention described herein for purposes of illustration, when the pocket comes into direct communication with the pressure port. It is thus apparent that the backpressurizing phase occupies only a short part of the pumping cycle of each pocket.

The fluid which is utilized to develop the backpressure by flow through restrictors 88 and 91 is advantageously mixed with the main volume of outlet fluid in passageway 54, for delivery to the outlet coupling 56. The percent of total output volume which is diverted through the restrictors is minor and may be on the order of magnitude of 10% or less.

Asgpreviously indicated, the ow diverting channels 82 have been found to have an especially desirable effect in conjunction with the backpressurizing structure of this invention. In particular, when a vane is traversing a transfer zone, these channels establish good fluid communication between the space behind the vane and the inner end 48 of the vane slot. As seen in FIGURE 5, pressure developed in the pocket between two vanes as pocket volume decreases is applied inwardly to the bottom of the vane slots through this channel 82, where it is applied to the check valve 78, 79.

Careful analyses have indicated that in a pump of the type shown in the drawings, the volumetric capacity of the piston pressure chamber 71 fluctuates, as the vanes rotate, by reason of the different numbers of vanes on the ramps at different rotor positions. This change in volumetric capacity is seen as a ripple in FIGURE 12B. We have found that the volume of the piston pressure chamber 71 is in fact decreasing as the vane starts to traverse a suction ramp (see FIGURE 12B). It might be expected that this decrease in the capacity of chamber 71 would increase the pressure on the fluid therein, since that uid is essentially trapped by the closed check valves 78, 79. However, our studies have shown that under low outlet pressure conditions, chamber 71 is not always completely filled with uid even when its rvolumetric capacity is decreasing. For example, there may be some foam or air bubbles therein, so that the decrease in volume does not of itself pressurize chamber 71. Backpressurizing causes chamber 71 to be lled with uid and establishes a minimum pressure therein which is in excess of outlet pressure, so that sucient force is applied to the actuating surfaces associated with the vanes to hold the vanes in contact with the cam surface, including the vane at the suction ramp.

Furthermore, additional pressure to provide increased force is produced by intermittent intensification of the pressure in chamber 71 as its volumetric capacity decreases. As can be seen from FIGURES 12A and 12C, chamber pressure begins to intensify before a vane comes onto the suction ramp. This intensification creates a force on the vane actuating means suicient to satisfy the deficiency illustrated by the shaded portion of FIGURE 12E.

Chamber 71 should preferably be sized such that the pressure therein is intensified sufficiently to insure proper tracking, but not so high as to produce excessive vaneto-cam ring loading which could damage the pump. In other words, chamber 71 serves as an accumulator as well as a conduit interconnecting the several vane inner actuating surfaces. The chamber 71 described herein differs from previous piston chambers in that the previous chambers were too small to limit intensification and therefore vane tip and cam ring wear resulted. The chamber 71 of this invention may have as much as four times the volumetric capacity of conventional piston grooves.

The new chamber also serves to store, as an accumulator, a minimum pressure in excess of normal outlet pressure. In practice it is preferred that the chamber 71 be sized to maintain pressure therein ranging between 1000 and 1500 p.s.i. greater than the minimum outlet pressure. Prior art chambers were too small to effectively store any such useful volume under pressure.

FIGURE 13 shows how the displacement rate from the pocket varies as the pocket moves through the backpressurizing phase of the cycle, from the transfer zone into the pressure zone. Displacement rate is essentially constant up to the beginning of the pressure zone. Displacement of fluid through the variable area restrictor 91 begins when the lead vane of the transport pocket comes onto the pressure ramp. The increasing flow rate as that occurs is indicated by the upward rise of the curve in FIGURE 13. Unrestricted flow to the pressure port does not begin at the moment the leading vane comes onto the pressure ramp, but preferably only after a portion of the fluid in the pocket has been displaced through the restrictor 91. This prolongs backpressurizing to insure that pressure in chamber 71 is maintained at a sufficiently high level t0 insure that the force on the pistons of the vanes, including those still on the suction ramps, is applied long enough to avoid vane skipping.

The structure above described illustrates a preferred form of the invention as incorporated in a three-area pump. In FIGURE 14 there is illustrated a two-area pump in which structure in accordance with the invention has been provided.

The two-area structure shown in FIGURE 14 has several elements which may be the same as or similar to elements previously described in connection with the three-area pump embodiment, and similar elements are therefore similarly numbered. Thus, in FIGURE 14 the configurations of cam ring 14, pressure ports 51, 52 and suction ports 43, 44 are similar to those illustrated and described in connection with FIGURE 3. Also, for purposes of reversing the direction of rotation of shaft 6, the cam ring is provided with recesses 59, 60 which coact with the cheek plate pressure ports 51, 52 in the same manner as previously described.

The cartridge of the structure shown in FIGURE 14 differs in that no hydraulic pistons are provided to actuate the vanes 101 in their slots, and in that the inner ends 102 of the vane slots are interconnected by annular grooves or pressure chambers, one of which is seen at 104, formed in the opposite side faces of the rotor. Also, there are no under vane suction ports corresponding to those designated at 47 in the three-area embodiment. This isolates pressure chamber 104 and the inner ends 102 of the vane slots from the suction ports.

The vanes 101 are single lip vanes; that is, they do not have the two lips separated by the edge groove of the vanes previously described. Also, these vanes are not provided with a passage corresponding to the channels or grooves 82. In this two-area pump pressure acts inwardly on the outer end surface or first area of the vane, and is opposed by pressure of uid in the inner end 102 of the` vane slot, acting on the inner end 105 or second area of the vane, and actuating the vane outwardly.

Openings 89 in the transfer zones 37 between the suction and pressure ports lead through flow restrictors (shown diagrammatically at y88 in FIGURE 14) to the pressure outlet port on coupling 56 of the pump. Each opening 89 is provided with a tapered slot extension 90 similar to those previously described. Preferably the tip or apex of the slot 90 extends just past the trailing side of the upstream vane of a pocket when the trailing vane of that pocket has just sealed the suction port. This optimum condition provides a path for the displacement of fluid when the volume of the closed pocket begins to be reduced by the lead on the cam surface in the transfer zone.

The pressure upstream of orce 88 is applied into the grooves 104 by passage means such as that designated diagrammatically 107. This pressure acts on all the vanes and urges them outwardly.

Where, as shown, the pump is reversible, similar flow restricting passages are provided on the other, or downstream, side of each press-ure port 51, 52. One way or check valve means 108 are provided in each passage 107, so that fluid is admitted into groove 104, but not released therefrom, through whichever opening 89 is under the higher backpressure. Thus, the other openings 89 on the other side of the pressure port comes into effect only when the direction of rotation of the pump is reversed, and as before, can be omitted in a single directional pump.

A variable area flow restrictor 91 extends from the leading edge of the pressure port. Preferably the apex of the tapered V-groove 91 is positioned so that when the lead vane of a pocket just comes onto the pressure ramp and is displaced inwardly thereby, pressure fluid from the pocket can just then be released through this restrictor directly to the outlet port. That is, the apex of groove 91 extends just past the back side of the lead vane when that Vane begins to track on the pressure ramp.

In the operation of the two-area embodiment shown in FIGURE 14, the slight inward lead on cam surface 34 over the transfer zone reduces the volume of a transport pocket moving therepast. If, as is preferred, the amount of this lead is constant, then the rate of displacement of fluid through the constant area restrictor 88 will be constant and consequently a constant backpressure is maintained in the pocket. That pressure is applied through passage 107 and check valve 108 into groove 104. Pressure in groove 104 acts on the inner ends 105 of all of the vanes and urges them outwardly. Restrictor 88 should preferably be sized so that the backpressure will be just sufficient to prevent skipping of the vane as it moves over the suction ramp. Similarly the cross sectional area of V-slot 91 is preferably sized to maintain a backpressure in the transport pocket, and hence in slot 104, substantially constant when the lead vane is cammed inwardly as it tracks on the pressure ramp.

The precise locations for the restrictors 88 and 91 disclosed herein are optimal for best timing, but obviously departures can be made from these optimums while still retaining at least part of the benefits of the invention. It will also be apparent that either of the restrictors 88 or 91 can be used alone, and will still provide backpressurizing though results may not be optimized. What is important, is that an internal backpressure be supplied which is sufficient in magnitude to apply the necessary pressure force to the vane actuating means for a period suicient to insure adequate vane tracking.

From the foregoing, those skilled in the art will understand that by this invention we have provided a method independent of external pressure, for backpressurizing the hydraulic vane actuators by displacement through flow restricting means of a minor portion of the fiuid between each pair of vanes, in a manner requiring minimal power even at idling conditions yet which is effective to avoid the chop previously encountered at low output pressures. Moreover, since the backpressurizing eect is based on flow through a restricted orifice, it inherently provides the greater forces on the actuating means which are required as pump speed increases, or as oil viscosity increases.

While we have described the invention herein in terms of a preferred embodiment, those skilledin the art will recognize that the invention can be employed in other specific structures, within the scope and spirit of the following claims.

What is claimed is:

1. A method of improving vane tracking in a vane pump having hydraulic pressure actuated vanes, when the pump outlet pressure is insufficient to supply the pressure force necessary to hold the vanes in contact with the cam surface, said method comprising,

diverting the flow of only a minor portion of the pump output volume being delivered by a transport pocket to a pressure port which opens to the pumping chamber, and restricting said ow to establish a backpressure in said transport pocket which is higher than the pressure on the major portion of the output volume at said pressure port which opens to said pumping chamber,

and applying said backpressure to an actuating surface associated with each vane to hold the vane into contact with the cam surface. 2. The -method of claim 1 further wherein said minor portion of the pump output volume, after being restricted in its flow, is merged with the major portion of the out-put volume and both said minor and major portions are delivered together to an outlet port.

3. The method of claim 1 further wherein said backpressure is applied to all of the actuating surfaces simultaneously.

4. The method of claim 3 further wherein said backpressure is applied to said actuating surfaces simultaneously by admitting said backpressure to a chamber interconnecting all said actuating surfaces, and blocking reverse flow of pressure fluid out of said chamber.

5. A method of improving vane tracking in a vane pump having hydraulic pressure actuated vanes, when the pump outlet pressure is insufficient to supply the pressure force necessary to hold the vanes in contact with the cam surface, said method comprising,

diverting the flow of only a minor portion of the pump output volume and restricting said flow to establish a backpressure which is higher than the outlet pressure on the major portion of the output volume,

applying said backpressure to an actuating surface associated with each vane to hold the vane into contact with the cam surface, said backpressure being applied to said actuating surfaces simultaneously by admitting said backpressure to a chamber interconnecting all said actuating surfaces, and blocking reverse flow of pressure fiuid out of said chamber.

the volume of said chamber being varied during the pumping cycle by non-offsetting movements of said actuating surfaces,

the iiow of said minor portion of the pump output volume being restricted when the volume of said chamber is increasing, the said restriction on the flow of said output volume being by-passed when the volume of said chamber is decreasing.

6. The method of claim 5 further wherein said minor portion is diverted through flow restricting means by moving fluid within said pump through a transfer zone which is progressively reduced in size as said fluid approaches the pressure port of said pump.

7. The method of claim 6 further wherein said transfer zone is reduced in size at a substantially constant rate as said fluid approaches the pressure port of said pump.

8. The method of claim 5 further wherein said backpressure is intensified to a higher pressure in said chamber by reducing the volume of said chamber.

9. The method of claim 8 further wherein sufficient fluid under pressure is stored in said chamber to limit the amplitude of pressure fluctuations therein resulting from the variation of volume of said chamber.

10. A hydraulic vane pump having vanes mounted by a rotor for engaging a cam surface,

a pressure port and a suction port opening at spaced positions to a pumping space defined between the rotor and said cam surface,

hydraulic vane actuating means associated with each vane for applying a pressure force to the vane in a direction toward said cam surface,

internal means within said pump for establishing a pressure which isrhigher than the pressure at the pressure port which opens to said pumping space,

and means for applying the higher pressure lto said actuating means to hold the -vanes in contact with the cam surface.

11. A vane pump in accordance with claim 10, wherein said pump includes a chamber interconnecting all of said actuating means,

one-way valve means for admitting pressure fluid into said chamber and preventing the release of uid therefrom,

and wherein the volume of said chamber is Varied during the pumping cycle by non-offsetting movements of said actuating means, thereby resulting in intermittent intensification and reduction of pressure in said chamber.

12. A vane pump in accordance with claim 11 wherein said chamber has sufficient volumetric capacity that it acts as an accumulator and limits the amplitude of the pressure intensification and reduction therein.

13. A vane pump in accordance with claim 12, wherein said chamber has a volumetric capacity such that pressure therein is intermittently intensified above the pressure admitted thereto through said one-way valve means, sufficiently to provide force on the actuating means during critical periods of the cycle.

14. A hydraulic vane pump having vanes mounted in a rotor for engaging a cam surface,

a pressure port and a suction port opening at spaced positions to the pumping space between said rotor and said cam surface,

an alternate transfer zone and a sealing zone in said pumping space between said pressure port and said suction port,

said cam surface having an inward ramp thereon over at least a portion of said transfer zone, said ramp reducing the volume of a transport pocket between a pair of vanes while said pocket is moving therepast,

a fiow restricting port opening to a transport pocket moving past `said ramp, through which port fiuid is displaced from said pocket by the reduction in volurne of said pocket,

and passageway means applying the pressure of fluid in said pocket moving past said ramp to operate hydraulic vane actuating means associated with all of said vanes for applying a net outward pressure force urging the vanes toward lthe cam surface.

15. A hydraulic vane pump in accordance with claim further wherein said flow restricting port connects said transfer zone to said pressure port.

16. A hydraulic vane pump in accordance with claim 15,

further wherein said flow restricting port is shaped to provide a substantially constant backpressure in said pocket during the period of displacement of liuid through it.

1,'7. A hydraulic vane pump h-aving vanes mounted in a rotor for engaging a cam surface,

a pressure port and suction port opening respectively into spaced pressure and suction Zones in the pumping space between the rotor and said cam surface,

a transfer zone and a sealing zone in said pumping space alternately between said pressure zone and said suction zone,

hydraulic pressure operated pistons associated with the respective vanes for applying force thereto actuating the vanes toward the Cam surface,

a pressure chamber interconnecting all of said pistons for applying equal pressures thereon,

said cam surface having an inward ramp over at least a portion of said transfer zone which reduces the volume of a transport pocket between a pair of vanes while said pocket is moving therepast,

a ow restricting port opening to said transfer zone, through which uid is displaced by the reduction in volume of said pocket,

and passageway means applying the pressure of fluid in said pocket into said pressure chamber.

18. The hydraulic vane pump of claim 17 wherein said passageway means includes one-way valve means for admitting pressure uid into said chamber and restricting the release of uid therefrom.

19. The vane pump of claim 17 wherein said ow restricting port is defined by a passageway Iopening from said transfer zone through an orifice to said pressure port,

and further wherein a tapered slot extends from said opening to a point in said transfer zone at which the reduction in volume of said pocket begins.

20. A vane pump in accordance with claim 17,

further wherein said cam surface has a pressure ramp thereon in said pressure zone, said pressure ramp having an inward lead thereon more pronounced than the ramp in said transfer zone,

and further wherein said pressure port opens to said pressure zone at a position downstream of the start of said pressure ramp,

and further wherein a second flow restricting port opens into said pressure zone upstream of said pressure port, through which second flow restricting port fluid is displaced by the reduction in volume of a pocket as the upstream vane of the pocket moves on said pressure ramp. 4

21. The vane pump of claim 20 wherein said second cflow restricting port has an increasing area opening to said pocket as the upstream vane of said pocket moves along said pressure ramp.

22. The vane pump of claim 21,

further wherein said second flow restricting port is defined by a tapered V-groove leading to said pressure port, said V-groove extending to a point such that it rst communicates with said pocket when the upstream vane of said pocket first comes onto said pressur ramp. v

23. The vane pump of claim 17,

further wherein each vane is provided with a passageway on its rear face for applying pressure fluid from said pocket to one-way valve means in said passageway means for admitting pressure fluid into said chamber and restricting the release of uid therefrom.

24. A hydraulic vane pump having vanes mountedby a rotor for engaging a cam surface,

a pressure port and a suction port opening at spaced positions to a pumping space dened between the rotor and said cam surface,

hydraulic vane actuating means associated with eachl vane for applying a pressure force to the vane in a direction toward said cam surface,

a chamber interconnecting al1 of said actuating means,

one-way valve means for admitting pressure uid into said chamber and preventing the release of iuid therefrom,

the volume of said chamber varying during the pumping cycle by non-offsetting movements of said actuating means, thereby causing intermittent intensification and reduction of pressure in said chamber,

said chamber having sufficient volumetric capacity that it acts as an accumulator and limits the amplitude of the pressure intensification and reduction therein.

References Cited UNITED STATES PATENTS 2,739,5 39 3/ 1956 Gardiner.

2,755,741 7/1956 Erskine.

V2,782,718 2/1957 Pettibone.

2,809,593 10/1957 Klessig et al.

2,832,293 4/1958 Adams et al. 103-202 X 3,072,067 1/1963 Beller.

3,223,044 12/1965 Adams et al. 91-138 X 3,401,641 9/1966 Adams et al 103-136 DONLEY J. STOCKING, Primary Examiner WARREN J. KRAUSS, Assistant Examiner 

